How a Glob of Fat the Size of a School Bus Got Stuck in the London Sewers

Blame the wet wipes.

For a vivid, smelly lesson on why we don’t pour bacon grease down the drain, behold the fatberg.

Last week, officials at Thames Water removed a 30,000-pound lump of lard from a trunk line sewer beneath the London suburb of Kingston. It was the fattest fatberg ever recovered from the London sewers, and by extension, probably the largest subterranean grease clump in U.K. history.   

TW CCTV fatty sewer image. Courtesy of Thames Water

"A fatberg," says Simon Evans, media relations manager at Thames Water, "is a vile, festering, steaming collection of fat and wet wipes." Fatberg creation is a vicious cycle, according to Evans, who coined the term. "Fat clings to wipes, wipes cling to the fat," he explains. "They are the catalysts in this horrible fatberg game."

The result, which feels like wax and smells much worse, is a major headache for metropolitan sewer authorities. Every month, Thames Water spends $1.5 million cleaning FOG (fat, oil and grease) deposits from Greater London’s 70,000 miles of sewers. In the U.S., FOG is responsible for about 40 percent of sewer blockages.

The offending fatberg. Courtesy of Thames Water

It took sewer flushers three weeks to blast apart London’s 15-ton fatberg with high-pressure water jets. The heap had blocked 95 percent of a trunk line sewer, and was discovered after residents reported they were having trouble flushing their toilets. If left undiscovered, the fatberg could have caused raw sewage to bubble up through manholes and household drains.

Evaluating the significance of last week’s events requires some semantic precision. "We have cleared greater volumes of fat and wipes out of a sewer before," Evans says, by way of clarifying, "but this was the largest single congealed lump of lard." While this fatberg has made headlines, in other words, it is but a fatcube compared to the 1,000 tons of FOG and wipes that were removed from beneath London’s Leicester Square in 2010.

Help, of sorts, is on the way. In 2015, London plans to open a fat-fueled power station at Beckton, which would turn the contents of local grease traps into energy to power London’s wastewater treatment. That, Evans says happily, will mark the start of the London fat-harvesting program, which could be a model for other large cities.

"Dewatered material" from a sink-based fat trap produces more energy than its weight in wood, and can have nearly the same energy potential as coal. But it’s only useful before it’s flushed down and blended with raw sewage and other unsavory materials like wet wipes.

While grease traps can eliminate the glue that holds the fatberg together, particularly by targeting worst-offender establishments like fast food restaurants (New York City requires restaurants to install the traps), the other "partner in sewer abuse," wet wipes, is harder to attack.

The moist towlettes have become an increasingly popular substitute for toilet paper in the U.K., with sales rising by double digits each year. The trend hasn’t quite caught on the U.S., but some corporations are trying to help it along: one out of every ten Americans adopting the practice would create a billion-dollar market… and a million dollar nightmare for sewer officials.

Sewer managers can only plead with residents to be more conscientious. "Bin it – don’t block it," says Evans.

Top image: Oliver Sved /Shutterstock.com

About the Author

  • Henry Grabar is a freelance writer and a former fellow at CityLab. He lives in New York.